Overview of JRA
Juvenile rheumatoid arthritis (JRA), also called juvenile idiopathic arthritis, juvenile chronic arthritis, and Still's disease, is the most common form of childhood arthritis in the United States. JRA is defined as joint inflammation lasting 6 weeks or longer in children under the age of 16.
JRA is often a mild disorder that causes few problems over time, but some children who have the condition experience significant joint and tissue damage. In severe cases, juvenile rheumatoid arthritis can result in serious complications.
JRA is thought to be an autoimmune disease, which means that the body's immune system does not recognize normal cells and attacks them. Juvenile rheumatoid arthritis affects the lining of the joint (called the synovial membrane), leading to inflammation (e.g., swelling), pain, and joint damage.
Types of JRA
There are three types of JRA:
- Pauciarticular juvenile rheumatoid arthritis affects children in early childhood and accounts for about 50% of cases. In this type, four or fewer joints are affected at the time of disease onset. Pauciarticular (pronounced paw-see-art-ik-u-lar) arthritis usually affects larger joints, such as the knees.
- Polyarticular juvenile rheumatoid arthritis occurs throughout childhood and adolescence and accounts for approximately 40% of cases. This type affects five or more joints, typically the smaller joints of the hands and feet. Polyarticular arthritis often affects the same joint on both sides of the body (i.e., is symmetrical).
- Systemic-onset juvenile rheumatoid arthritis usually occurs in early childhood, but can extend into adolescence. This type accounts for about 10 percent of cases and affects many areas of the body, including joints and internal organs.
Incidence and Prevalence of JRA
Exact incidence and prevalence of juvenile rheumatoid arthritis are difficult to determine. It is estimated that childhood arthritis affects as many as 300,000 children in the United States. JRA is approximately twice as common in girlswith the exception of systemic-onset disease, which affects girls and boys about equally. JRA may occur more frequently in certain populations (e.g., Native Americans) and rates vary by geographical location, which may indicate an environmental risk factor.